A mass spectrometer which is used to analyze a residual gas in a EUV lithography apparatus and which has an ion trap for storing the at least one contaminating substance is known from WO 2010/022815 A1.
Mass spectrometry is used not only in EUV lithography but also in many further fields, for example for characterizing chemical compounds in medical chemistry, for identifying substances in bodily fluids or organs, in forensic examinations, doping tests or military analysis of chemical weapons, etc. It is also used for residual gas analysis in pharmacokinetics and in vacuum technology.
In the mass spectrometric examination of gaseous substances or gas mixtures, the mass, more precisely the mass-to-charge ratio, of atoms or molecules is determined in order to obtain a chemical characterization of the gaseous substances. The substances to be examined or the substance mixture to be examined is either already available in the gaseous phase or is converted to the gaseous phase in order to be ionized via an ionization unit. In conventional mass spectrometers, the substances ionized in this manner are supplied to an analyzer and are typically guided through an electric and/or magnetic field, in which the ions describe characteristic trajectories due to different charge-to-mass ratios and it is therefore possible to distinguish between them.
Due to the disadvantages of currently available mass spectrometers, such as large dimensions, slow scanning measurement, no particularly high sensitivity, etc., some known mass spectrometers can only be used to restricted extent, or even not at all, in many applications.
By way of example, the stability of a measurement signal from a gas analyzer or mass spectrometer depends strongly on the temporal stability of the ionization. Conventional quadrupole mass spectrometers generally operate using hot-filament ionization and typically have an inaccuracy of approximately 10%-20%. Alternative types of ionization, such as e.g. plasma ionization, which can likewise be used in mass spectrometry, generally have an inaccuracy in the region of 5%-10% due to inaccuracies in the plasma gas regulation and/or fluctuations in the plasma power.
The time-dependent fluctuations during the ionization lead to a proportional variation in the measurement signals, which entails a corresponding inaccuracy of the measurement. This inaccuracy is particularly disadvantageous if the gas analyzer or the mass spectrometer is intended to be used for quantitative measurements and/or for monitoring and/or examining gas-phase processes in the semiconductor industry or in the chemical industry.
Moreover, during measurements in many conventional mass spectrometers, such as e.g. quadrupole mass spectrometers, the masses are scanned in succession, leading to a long measurement time which, in the case of a high-resolution measurement, can lie in the region of a plurality of minutes, and even in the region of a plurality of hours.
In order to be able to detect a small amount of analytes, i.e. gas constituents to be detected, in a residual gas or process gas under high pressure, there is a need for a large dynamic range. In general, conventional mass spectrometers only enable a dynamic range (ratio of maximum measurable signal to minimum measurable signal) of approximately 106 to at most 107.
In order to detect a small amount of analytes in a residual gas, it is desirable for the mass spectrometer to have a very low detection limit. Currently available mass spectrometers achieve a detection limit of 10−13 mbar to 10−14 mbar. For the sensitive detection, use is often made of charge multipliers, which have a large amount of scattering of more than 20% and moreover typically cannot be used at relatively high pressure (>10−4 mbar).
Moreover, mass spectrometers are used for different application cases with different pressure ranges of the analyte and/or the background gas. Commercial mass spectrometers are typically designed for one pressure range or the other, but there are no mass spectrometers which cover a very large pressure range without a complicated pressure-specific reconfiguration having to be undertaken for this purpose.